My dealer in Missoula thought it was a poor quality belt. When he examined it he said it "delaminated" and came apart.
The Harley belt I put on there in 2005 was still going strong when I sold the belt and pulleys. And it had taken some abuse. I gave a ride to a rather hefty date one time, just a short jaunt down the road. Well, clearly my bike was overloaded and we hit one bump. Blew out the rear shocks and my home-made saddle bracket scored the center of the belt all the way around. Since the damage didn't cross the edge it was fine. Tough stuff.